It is only close up that his secret is revealed: a faded, 12-inch scar running from his breastbone to his pelvis, the sole evidence of the day he nearly died in January 2009.

Mears had been competing in the Youth Olympic Festival in Sydney when, at breakfast one morning, he collapsed. At first he was diagnosed with sunstroke, then meningitis: both were wrong. He had contracted the Epstein Barr virus and had ruptured his spleen while performing a dive the previous day.

The prognosis from his surgeon at Sydney’s Royal Prince Alfred Hospital, delivered by telephone to his frantic mother, Katy, back home in Reading, was dire. Mears had lost five pints of blood and was given less than a five per cent chance of survival. Even when his spleen was removed, a series of convulsing fits left his life hanging by a thread.

With his family at his bedside, he spent a month in hospital, slowly regaining his strength for the 24-hour flight home. Three years later, Mears, who lost three stone and most of his muscle mass in hospital, is able to reflect on those desperate weeks as not simply the moment his life was saved, but also the turning point in his diving career.

“The experience changed me, and so much for the better,” he said. “Before the Games I was still at school and had other things I was concentrating on, but when this happened I knew what I wanted to do straight away. As soon as I came back to England I said to my coach, 'I want you to make me an Olympic diver’. And my dream has almost come true.”

Mears, who was 19 earlier this month, will be competing in the three-metre springboard at this week’s Visa World Cup in the Olympic Aquatics Centre - the official test event for London 2012 and also the final qualifying competition for the Games.

With Jack Laugher having already qualified for one individual three metre berth for Britain, it will be up to Mears to secure a second by finishing in the top 18 in Tuesday’s preliminary round or, failing that, by sealing a spot in next Sunday’s dive-off for the last remaining places.

Whatever happens, the teenager is all but guaranteed his place in Team GB since Britain receives automatic host-nation places in all synchro events and he and partner Nick Robinson-Baker are the No 1 British pair in the men’s three metre.

Mears, who will be one of the first divers in action this morning when he and Robinson-Baker compete in the synchro preliminary round, says that when it comes to the real thing in London this summer, he expects his parents to be reaching for the tissues. “They recognise where I’ve come from and what a hard time I’ve had,” Mears said. “Every athlete has a story behind them but mine is slightly different. So, yes, they’re going to be really proud of me.”

In fact, theOlympics will mean a double honour for the Mears family since father Paul was nominated by the British Olympic Association to carry the Olympic Torch during the 70-day relay this summer in recognition of his and Katy’s long bedside vigil in Australia.

“It was a very hard time for me and a very hard time for my parents, so it’s good to be rewarded,” Mears said. “My dad is absolutely ecstatic about it. He’s even doing a little bit of training to run with the torch because he hasn’t run in a while.”

Another visitor to Mears’ bedside in Sydney was Australia’s Olympic 10m platform champion, Matt Mitcham, who brought in his gold medal for Mears to try for size.

“That was amazing,” Mears said. “I was only 15 and I admired all the divers on the world circuit, so it was great to see him.”

The fact that he and Mitcham will both be in action in London this week is a reminder of how far he has come in the past three years. Mears insists he is taking none of it for granted. “You think to yourself, 'I couldn’t even be on this planet any more. I could be somewhere else’. I know that sounds bleak but I’ve turned it into a positive.”